Standedge - Longest, Deepest, Highest

The Standedge canal tunnel, on the Huddersfield Narrow Canal, is one of four parallel tunnels - the other three are railway tunnels - that run through the Pennine hills between Marsden, West Yorkshire, and Diggle, Greater Manchester. The Act of Parliament authorising the canal's construction was passed in April 1794. Benjamin Outram, acting as consulting engineer, estimated the total cost, including the tunnel, at £178,478, and the construction period at five years. Nicholas Brown undertook the necessary survey work, which foresaw a tunnel of 5,456 yards.

Outram was appointed site engineer, and Brown surveyor and superintendent. The tunnel was driven from both ends at once and from intermediate shafts. The intermediate workfaces were abandoned in the autumn of 1796. This change, greater water ingress than expected, and difficult geology, slowed progress. The rest of the canal was completed by 1799, and horses used to transship cargo over the Pennines between the completed sections. Tenders for work on the tunnel went unlet, and it was found that the headings had been driven several feet higher from the Diggle end than from the Marsden (above). In 1801 Outram resigned and Brown was dismissed.

In 1806 a new Act of Parliament provided for the raising of further finance. Thomas Telford was consulted, and in 1807 drew up a plan for completion. This corrected for the crooked workings driven from the intermediate headings: the tunnel has noticeable bends. Finally completed in March 1811, and at a cost of £123,803 for the tunnel alone, this was 5,445 yards (3.1 miles) long, 636 feet below ground at its deepest, and 643 feet above sea level. The longest, deepest and highest canal tunnel in the UK.

In 1822 the tunnel was extended 11 yards at the Marsden end, to accommodate reservoir works. In 1893 it was extended again, by 242 yards, this time at the Diggle end, so that the 1894 railway tunnel could be carried over it. These additions supposedly made the tunnel 5,698 yards long, although modern survey techniques make the total length 5,675 yards (3.2 miles).The tunnel has no towpath, which required the canal boats to be legged through. This was tough and dangerous work, not least given that large parts of the tunnel were left unlined, with the native rock jaggedly proud of the ever-changing overall profile. Some sections are lined with rough-dressed stone, and some with brick.

The Huddersfield and Manchester Railway bought the canal in 1846, which enabled the first railway tunnel, completed 1848, to be driven without the need for ventilation or extraction shafts. Drainage adits (above) drain the higher railway tunnels into the canal tunnel, and gantries (below) link the former. When the railway tunnels were driven much strengthening work of the canal tunnel was required in the form of heavy brick arches.

The tunnel officially closed in 1944, when maintenance ceased. Dilapidation prevented all but a couple of later exploratory journeys. A £5m restoration project in the 1990s set about reopening the canal in its entirety. Shotcrete and rock-bolting were used to stabilise some of the unlined sections of the tunnel. This reopened in May 2001, after 57 years of disuse. Boats were tugged through by electric tugs, but since 2009 have been able to transit the tunnel under their own power, with a pilot aboard, and chaperoned by a vehicle driven through the adjoined first railway tunnel (below). The journey takes about two hours.